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Ch 10 – Forensic Toxicology

Ch 10 – Forensic Toxicology. Alcohol in the bloodstream. Human circulatory system. Alcohol excretion in the breath. Breathanalyzer. Chemical equations. Infrared breath-testing device. Field sobriety tests. Alcohol concentration in blood. . Blood alcohol in your state.

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Ch 10 – Forensic Toxicology

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  1. Ch 10 – Forensic Toxicology • Alcohol in the bloodstream. • Human circulatory system. • Alcohol excretion in the breath. • Breathanalyzer. • Chemical equations. • Infrared breath-testing device. • Field sobriety tests. • Alcohol concentration in blood.

  2. Blood alcohol in your state. • Significance of the implied consent law and the Schmerber v. California case to trafic enforcement. • Acids and bases. • Role of toxicologist in the criminal justice system. • Techniques of isolating and identifying drugs and poisons. • Finding a drug in human tissues and organs.

  3. Collaboration between Drug Recignition Expert and Forensic Toxicologist in positive drug finding. http://www.fbi.gov/hq/lab/handbook/examtox.htm http://www.abarbour.net/ http://home.lightspeed.net/~abarbour/labs.htm http://faculty.ncwc.edu/toconnor/425/425lect14.htm http://www.lib.uiowa.edu/hardin/md/tox.html

  4. Absorption: passage of alcohol across the wall of the stomach and small intestine into the blood stream • Oxidation: the combination of oxygen with other substances to produce new products • Excretion: elimination of alcohol from the body in an unchanged state; alcohol is normally excreted in breath and urine

  5. Artery: a blood vessel that carries blood away from the heart • Vein: a blood vessel that transports blood toward the heart • Capillary: a tiny blood vessel across whose walls exchange of materials between the blood and the tissue takes place; receives blood from arteries and carries it to veins

  6. Alveoli: small sacs in the lungs through whose walls air and other between the breath the breath and the blood • Catalyst: a substance that acceleration the rate of a chemical reaction but is not itself permanently changed by the reaction • Fuel cell: a detector in which chemical reactions are used to produce electricit

  7. Anticoagulant: a substance that prevents coagulation or clotting of the blood • Preservative: a substance that stops the growth of microorganisms in blood • Metabolize: transforming a chemical in the body to another chemical for the purpose of facilitating its elimination from the body • Acid: a compound capable of donating a hydrogen ion (H+) to another compound

  8. Base: a compound capable of accepting a hydrogen ion (H+) • pH: a symbol used to express the basicity or acidity of a substance. A pH of 7 is neutral; lower values are acidic and higher values are basic

  9. Ch. 10 - Forensic Toxicology Alcohol

  10. What is Toxicology? • Toxicological examinations involve the identification and often quantitation of drugs & toxic materials in the human body • The role of the forensic toxicologist is limited to matters pertaining to violations of criminal law • determination of the presence of alcohol in the body • identification of substances causing unnatural death

  11. Toxicology of Alcohol The Fate of Alcohol in the Body

  12. Properties of Alcohol • Alcohol is a general term for a family of organic compounds • commonly encountered memebers include methanol, ethanol, isopropanol • The term alcohol will be taken to mean ethanol (ethyl alcohol)

  13. Chemical Properties of Ethanol • A clear volatile liquid • Burns easily • oxidizes easily • Slight, characteristic odor • Is very soluble in water • miscible in all proportions

  14. Physiological Properties of Ethanol • A central nervous system (CNS) depressant • CNS is the bodily system which is most severely affected by alcohol • The degree to which the CNS function is impaired is directly proportional to the concentration of alcohol in the blood

  15. What Does the Body Do With Alcohol? • When an alcoholic beverage is swallowed, it is diluted by stomach juices & quickly distributed throughout the body • Alcohol does not require digestion before its absorption into the bloodstream • some diffuses into bloodstream directly through the stomach wall • remainder passes into the small intestine • rapidly absorbed & circulated

  16. Alcohol Absorption • Alcohol is absorbed from all parts of the gastrointestinal tract largely by simple diffusion into the blood • small intestine is the most efficient region for absorption because of its large surface area • The rate of absorption varies according to the particular beverage & the state of the consumer’s stomach

  17. Alcohol absorption • Fasting individual • 20-25% of a dose of alcohol is absorbed from the stomach • 75-80% is absorbed from the small intestine • peak blood alcohol concentrations occur in 0.5-2.0 hrs

  18. Alcohol Absorption • Non-fasting individuals • presence of food in stomach (especially gatty foods) delays absorption • peak alcohol concentrations 1.0-6.0 hrs • Alcohol ingested with carbonated beverages • ordinarily absorbed more rapidly than straight alcohol

  19. Alcohol Distribution • Alcohol has a high affinity for water • Is diffused in the body in proportion to the water content of the various tissues & organs • greater concentration in blood & brain • lesser concentration in fat & muscle

  20. Alcohol Distribution • Absorbed alcohol is greatly diluted by the aqueous body fluids • 1 oz. (29.57 mL) of 50% (100 proof) whiskey will be diluted in a man of average build, to a concentration ~2 parts per 10,000 in the blood (0.02%)

  21. Blood Alcohol concentration • BAC is the amount of alcohol in the bloodstream measured in percentages • BAC = 0.10% • means a person has 1 part alcohol per 1,000 parts of blood in the body

  22. Elimination • Liver eliminate ~95% of the alcohol through metabolism • oxidation via acetaldehyde & acetic acid to carbon dioxide & water • Remainder of eliminated through excretion in breath, urine, sweat, feces, milk & saliva • Rule of Thumb • 0.5 oz (15 mL) alcohol eliminated per hr

  23. Blood Alcohol Concentrations • A set of probable average curves of BAC in an average-size man after rapid absorption of various amounts of alcohol • Shows rate of BAC decline over time as a result of metabolism & excretion

  24. Elimination • Absorbed alcohol is passed through the liver by circulating blood • ADH (alcohol dehydrogenase) converts the alcohol to acetaldehyde • acetaldehyde is a highly toxic substance • Aldehyde dehydrogenase converts acetaldehyde to acetate ion • Acetate enters blood stream & is ultimately oxidized to CO2

  25. Elimination • Both enzymatic reactions require a co-enzyme, NAD, which accepts a hydrogen from the molecule • The temporary depletion of NAD by the first step limits the rate at which alcohol can be metabolized

  26. Curve a • drinking 2 oz alcohol each hr for 4 hours • BAC increase is cumulative because alcohol is consumed faster than it can be metabolized • Curve b • drinking 8 oz all at once

  27. Affect of Body Mass One Hour of Drinking Two Hours of Drinking

  28. BAC’s Affect Behavior Alcohol in the bloodstream continually circulates to the brain

  29. Some Alcohol Statistics • ~half of traffic injuries involve alcohol • ~1/3 of fatally injured passengers & pedestrians have elevated blood alcohol levels • ~half of homicides involve alcohol • 1/2 to 1/3 of suicides involve alcohol • CDC estimates ~30,000 unintentional injury deaths are directly attributable to alcohol

  30. Alcohol & Driving Relative Fatality Risk(drivers in a single vehicle crash)

  31. Respiratory System • Volatile chemicals dissolved in the blood will be brought to equilibrium with the air in the lungs • fixed ratio between compound in breath & blood

  32. Alcohol in Blood vs Breath • The ratio of alcohol in blood to alcohol in alveoli air is 2100 to 1 • 1 mL of blood will contain about the same amount of alcohol as 2100 mL of breath • During the period of absorption, the alcohol concentration is higher in arterial blood than venous blood • breath test reflects alcohol conc. in the pulmonary artery (reflects what reaches the brain

  33. The Breathalyzer • Measures the alcohol content of alveolar breath • Subject blows into a mouthpiece until 52.5 mL of alveolar breath has been collected • measures alcohol concentration of 1/40 mL of blood • The alcohol in the blood is reacted with chromic acid

  34. Breathalyzer • Beers’ Law • the concentration of Cr (VI) is directly proportional to the amount of 420 nm light light absorbed by the sample • Measures the concentration of the unknown solution to the concentration of a standard sample

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